Simpson, hired trainer Mike Alexander, 27, her old pal from J.J. Pearce High School in Richardson, Texas, to change her diet and whip her into shape — even before she landed the role late last summer.

"Jessica wanted more of a bump for her rear end instead of a flat butt," says Alexander, who works at Beverly Hills' Sports Club LA. He trained Simpson there nearly every day — one hour with weights and a half-hour of cardio. To achieve a toned butt and legs, Simpson took on a rigorous program of lunges and squats while holding 7½-pound weights.

Alexander helped chisel her back, arms, shoulders and chest. "Most of the stuff she wore was sleeveless or strapless," he says. "We did a lot of bicep curls, 10-pound elbow cable extensions, incline press and shoulder raises."

Alexander lived in a house with Simpson during the three months she was in Baton Rouge last fall shooting Dukes. "I ate every meal with her so I could tell her what to order," says Alexander, who encouraged Simpson to eat grilled chicken, seared fish, broccoli and asparagus. She avoided bread baskets brought to the table and declined extra sugar for her iced tea. Free desserts brought to the table were refused.

What's missing from the program plan? A personal trainer. Nice if you can afford it.